Health monitoring:
- gitserver: /health endpoint on port 8021 (DB + Redis ping)
- git-hook: hyper health server on port 8083 with /health
- email-worker: hyper health server on port 8084 with /health
- K8s probes updated to httpGet for all three services
Metrics (via /metrics endpoint):
- git-hook: hook_tasks_total/success/failed/locked/retried/exhausted,
hook_sync_branches/tags_changed_total
- email: email_queued/consumed/sent/failed_total,
email_validation_skipped/build_errors/send_attempts_total
- session_manager/manager.rs: remove slog::Logger field, update new()
and with_config() to remove log parameter
- email/lib.rs: remove slog::Logger from AppEmail::init()
- rpc/admin/server.rs: remove slog::Logger from serve() and spawn(),
replace with tracing::info!/error!
